The present invention relates to solvent removal from water with hydrophobic aerogels, particularly to the preparation of hydrophobic organic aerogels, and more particular to synthetic methods for the preparation of hydrophobic organic aerogels.
The key property of the porous materials that inhibits wetting by liquid water, is hydrophobicity. This property requires that the interfacial energy of the solid-liquid, is greater than that for the solid-vapor. Such a property is inherent for many polymers; the best examples of which are polyethylene, and polytetrafluoroethylene (Teflon). Other material such as carbons and inorganic oxides, including aerogels, generally have low liquid-solid interfacial energies and their surfaces have to be chemically modified to make them hydrophobic.
Aerogels are a special class of open-cell foams derived from highly cross-linked inorganic or organic gels that are dried using special techniques to preserve the tenuous solid network. These materials have ultrafine cell/pore sizes, continuous porosity, high surface area, and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 100 Å. This microstructure is responsible for the unusual optical, acoustical, thermal, and mechanical properties of aerogels. By definition, these materials are prepared through the sol-gel process and can be either granular or monolithic. Organic aerogels are typically prepared from the sol-gel polymerization of resorcinol and formaldehyde and are dried through supercritical extraction of the reaction solvent. Recent efforts have focused on the ability to tailor the bulk properties of organic aerogels for specific applications. One area of interest is the design of hydrophobic organic aerogels.
While there are several reported ways to make hydrophobic silica aerogels, it has been found that silica aerogels which are doped with fluorinated organic groups exhibit the highest degree of hydrophobicity. By measurement of the contact angles for a variety of hydrophobic aerogels, including tri-methyl, tri-fluoro, and methoxy terminated siloxanes, it has been determined that the 3,3,3-trifluoropropyl containing aerogels have the highest contact angles for all cases of silica aerogels. It was found that silica aerogels doped with 30% by weight of the flouro-propyl compound, gave a contact angle ≧150°, and was transparent. Such hydrophobic inorganic or silica aerogels are described and claimed in copending U.S. application Ser. No. 09/957,854, filed Sep. 21, 2001, entitled “Method For Removing Organic Liquids From Aqueous Solutions and Mixtures”; Ser. No. 09/957,853, filed Sep. 21, 2001, entitled “Super-Hydrophobic Fluorine Containing Aerogels; and Ser. No. 09/960,593, filed Sep. 21, 2001, entitled “Method of Oil Spill Recovery Using Hydrophobic Sol-Gels and Aerogels”. Also, see L. W. Hrubesh, “Solvent Removal from Water with Hydrophobic Aerogels, J. Nanocrystalline Solids” 285 (1-3), 328-32, 2001, for the verification of hydrophobic silica aerogels.
The present invention involves the use of the hydrophobic organic aerogels for removal or organics from an oil-water mixture for example, and more specifically the present invention provides synthetic methods for the preparation of hydrophobic organic aerogels. One of these methods particularly involves the sol-gel polymerization of 1,3-dimethoxybenze or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Other of these methods involves the sol-gel polymerization of 1,3,5-trihydroxy benzene or 1,3-dihydroxy benzene and various aldehydes in non-aqueous solvents. These methods can be applied to a variety of other sol-gel precursors and solvent systems for producing hydrophobic organic aerogels.